
package com.feib.stms.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;


/**
 * @title (#)UnicodeReader.java<br>
 * @description changed BOM recognition ordering (longer boms first)<br>
 * Original pseudocode   : Thomas Weidenfeller<br>
 * Implementation tweaked: Aki Nieminen<br>
 * http://www.unicode.org/unicode/faq/utf_bom.html<br>
 * BOMs:<br>
 * 00 00 FE FF    = UTF-32, big-endian<br>
 * FF FE 00 00    = UTF-32, little-endian<br>
 * EF BB BF       = UTF-8,<br>
 * FE FF          = UTF-16, big-endian<br>
 * FF FE          = UTF-16, little-endian<br>
 * Win2k Notepad:<br>
 * Unicode format = UTF-16LE<br>
 * @version 1.0.0 2010/11/25
 * @copyright Far Eastern International Bank Copyright (c) 2010<br>
 * @2010/11/24 create by Jimmy Liu<br>
 */
public class UnicodeReader extends Reader {
	PushbackInputStream internalIn;
	InputStreamReader   internalIn2 = null;
	String              defaultEnc;

	private static final int BOM_SIZE = 4;

	/**
	 *
	 * @param in  inputstream to be read
	 * @param defaultEnc default encoding if stream does not have 
	 *                   BOM marker. Give NULL to use system-level default.
	 */
	UnicodeReader(InputStream in, String defaultEnc) {
		internalIn = new PushbackInputStream(in, BOM_SIZE);
		this.defaultEnc = defaultEnc;
	}

	public String getDefaultEncoding() {
		return defaultEnc;
	}

	/**
	 * Get stream encoding or NULL if stream is uninitialized.
	 * Call init() or read() method to initialize it.
	 */
	public String getEncoding() {
		if (internalIn2 == null) return null;
		return internalIn2.getEncoding();
	}

	/**
	 * Read-ahead four bytes and check for BOM marks. Extra bytes are
	 * unread back to the stream, only BOM bytes are skipped.
	 */
	protected void init() throws IOException {
		if (internalIn2 != null) return;

		String encoding;
		byte bom[] = new byte[BOM_SIZE];
		int n, unread;
		n = internalIn.read(bom, 0, bom.length);

		if ( (bom[0] == (byte)0x00) && (bom[1] == (byte)0x00) &&
				(bom[2] == (byte)0xFE) && (bom[3] == (byte)0xFF) ) {
			encoding = "UTF-32BE";
			unread = n - 4;
		} else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) &&
				(bom[2] == (byte)0x00) && (bom[3] == (byte)0x00) ) {
			encoding = "UTF-32LE";
			unread = n - 4;
		} else if (  (bom[0] == (byte)0xEF) && (bom[1] == (byte)0xBB) &&
				(bom[2] == (byte)0xBF) ) {
			encoding = "UTF-8";
			unread = n - 3;
		} else if ( (bom[0] == (byte)0xFE) && (bom[1] == (byte)0xFF) ) {
			encoding = "UTF-16BE";
			unread = n - 2;
		} else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) ) {
			encoding = "UTF-16LE";
			unread = n - 2;
		} else {
			// Unicode BOM mark not found, unread all bytes
			encoding = defaultEnc;
			unread = n;
		}    


		if (unread > 0) internalIn.unread(bom, (n - unread), unread);

		// Use given encoding
		if (encoding == null) {
			internalIn2 = new InputStreamReader(internalIn);
		} else {
			internalIn2 = new InputStreamReader(internalIn, encoding);
		}
	}

	public void close() throws IOException {
		init();
		internalIn2.close();
	}

	public int read(char[] cbuf, int off, int len) throws IOException {
		init();
		return internalIn2.read(cbuf, off, len);
	}


}
